Method of acidizing wells



led-'37 United States Patent ,157,232 METHGD fill AfilZlNG WELLS doseph Ramos, Homer Charles McLaughlin, In, and

Ronney l2. Koch, Duncan, tlldzu, assiguors to Hallibnrton Company, Duncan, Okla, a corporation of Delaware No Drawing. Filed dune 19, 1961, Ser. No. 117,838 17 Claims. (fill. 166-38) This invention relates to chemical treatments of 0il-' bearing earthen formations. More particularly, the invention pertains to an improved method of acidizing wells.

Various .such acidizing treatments and procedures are known, but normally when an oil well is acidized, acid is merely pumped into the well from a tank and out into the formation to be treated. The acid in transit during and before the treatment presents a corrosive problem to the metal portionsof the tank which are exposed to the acid solution. Similarly, on location the acid has a tendency to attack the pumps, the metal tubing leading to and within the casing as well as all of the necessary oil well tools and connecting lines. The expense of repairing URUiSS litt'htttilbt.

orreplacing the corrosion damaged parts is extremely high. j

It is a principal object of the present invention to provide an improved process of carrying on acidizing treatments of oil wells which are free of the foregoing disadvantages.

It is a further object of the present invention to provide a method of acidizing oil-bearing earthen formations which greatly decreases the corrosion problems discussed above. 7

Another object is to provide an improved method of acidizing oil-bearing earthen formations which comprises producing the desired acid on location by charging to the well, certain non-acidic non-corrosive chemicals which when reacted together will form the necessary acid.

Still another object of the present invention is to provide a new and improved method of acidizing oil-bearing earthen formations wherein certain non-acid, non-corrosive chemicals are combined in container at the well site and substantially immediately thereafter pumped into the well for providing the desired acid.

Delayed production of the acid on location at the Well head, or if desired, in a zone within the well in the vicinity of the oil bearing formation avoids the handling of corrosive acids prior to the exact moment when needed.

The-foregoing objects are attained in accordance with this invention by providing a method of acidizing oilbearing earthen formations to increase the productivity thereof which comprises charging formaldehyde into a well as a first reactant, and as a second reactant an ammonium salt capable of reacting with the first reactant to form a free acid, reacting said reactants and directing the acid formed into and through the oil bearing earthen formation.

This method involves a known reaction between an ammonium salt with formaldehyde and no claim of invention is made thereto. The general nature of the reaction is described, for example, by 3. Frederick Walker, in an American Chemical Society Monograph publication, 1953, entitled Formaldehyde, at pages l8l183 and Chapter 19, thereof.

The products of the reaction are hexamethylene tetramine and a free acid, and for example, when the ammonium salt is respectively ammonium chloride and ammonium nitrate the reactions would be represented as follows:

The different acids, hydrochloric and nitric are the condensation products of the foregoing reactions and they 3,l57,232 Patented Nov. l7, 1964 vary depending solely on the substitution of different ammonium salts. Thus, substantially any acid desired can be produced: for example, ammonium acetate yields acetic acid, ammonium citrate yields citric acid, ammonium formate yields formic acid, tetraammonium ethylenediamine tetraacetate yields ethylenediamine tetraacetic acid, ammonium fluoride or bifluoride yields hydrofluoric acid, ammonium nitrate yields nitric acid, ammonium sulfate yields sulfuric acid, ammonium carbonate yields carbonic acid, etc. The list could be extended to include any acid Whose ammonium salt is producible.

In view of the fact that neither the formaldehyde nor the ammonium salts present any substantial shipping or handling problems, such as the corrosiveness of acid solutions, a substantial economic and operational advantage is effected. A somewhat related advantage is that the hazardous and difficult to handle acids, such. as hydrofluoric and nitric, can conveniently be produced in accordance with this invention, at the well head or in a zone immediately'adjacent the oil bearing earthen strata or formation. The hazards and inconveniences which attach to handling these dangerous materials as in prior art methods are thus avoided.

Furthermore, acidizing methods utilizing the present delayed production of the acid have the advantage that the acid penetrates deeper or further back into the oilbearing zones and thereby is capable of reaching and releasing more of the desired mineral products. Heretofore, the effectiveness of the acid has been spent and .consumedin the areas immediately around the well bore.

One method in which the present invention may be used is as follows: A supply of formaldehyde solution is brought to the well site along with a supply of an ammo-' nium chloride salt. In the present instance regular tankcars are used, although any other suitable means might be employed to provide the chemicals. Two pumps of equal size .and capacity are connected to the tank cars and the reactants are discharged in stoichiometric equivalent amounts via supply lines to the well head. The reaction occurs as the reactants come into contact resulting in the acid being formed within the well from whence it is directed down into and throughout the oilbearing formation. I I

While the chemistry of theforeg'oing reaction depicted above indicates the formation of free hexamethylenetetramine; actually only three moles of the free acid are produced while the additional acid forms with the hexamethylenetetramine an acid complex hexamethylenetetramine hydrochloride C H Ni -HCL The foregoing embodiment can readily be modifiedby pumping one reactant, e.g. formaldehyde down the annulus of the well and the second reactant, e.g. the 'ammonium chloride salt, down the tubing and bringing the reactants together in the vicinity of the oil-bearing formation.

In addition to the embodiments expressed above, the two reactants may be mixed together or combined in containers prior to pumping or injecting the reactant solution into the well. When this procedure is followed, such reactant solution should be substantially immediately introduced into the well to achieve the desired result in acidizing the oil-bearing zone or formation.

In three typesof reactions between the formaldehyde and an ammonium salt, hexamethylenetetramine is formed along with the desired acid. The presence of hexamethylenetetramine has not been found to noticeably effect or retard the effectiveness of the free acid in its function of acidizing the mineral bearing earthen formation and thus increasing the productivity of the well.

Other materials may be added to the reactants which do not basically alter the desired formation of the acid. For example, as known in the prior art suitable bases such r 3 as ammonium hydroxide may be present to adjust the pH of the reaction and thereby control the speed of the reac tion. 7

While the foregoing detailed description and specific examples indicate preferred embodiments of the invention, they are given by Way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

1 WhatIis claimed is:

1. A" method of acidizing oil-bearing earthen formations to increase the productivity thereof which comprises charging a formaldehyde solution into a well as a first reactant, and, as a second reactant, an ammonium salt solution capable of reacting with the first reactant to form a free acid, contacting the first reactant with the second reactant thereby forming the free acid, and directing the acid formed into and throughout the oil-bearing earthen formation.

2. The method of claim 1 wherein the reactants are reacted in stoichiometric equivalent proportions.

an organic acid.

5. The method of claim 1 wherein the ammonium salt is selected from the group consisting of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium/bromide, ammonium carbonate, ammonium acetate, ammonium citrate, ammonium formate, and tetraammonium ethylenediaminetetraacetate.

"6. A method of acidizing an oil-bearing earthen formation in a well having an annulus and tubular members therein comprising the steps of, pumping a formaldehyde solution down the annulus of the well, and simultaneously pumping an ammonium salt solution capable of reacting with said formaldehyde to form a free acid down the tubular members whereby said formaldehyde solution and said ammonium salt solution are brought together at a predetermined position in the Well prior to entry in the oilbearing earthen formation, thereby forming the acid, and then pumping the acid into the formation.

4 1 mined position in the Well prior to entry in the oil-bearing earthen formation, thereby forming the acid, and then pumping the acid into the formation.

10. The method of claim 9 wherein said ammonium salt is selected from the group consisting of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium carbonate, ammonium acetate, ammonium citrate, ammonium formate, and tetraammonium ethylenediaminetetraacetate.

11. The method of claim 9 wherein said ammonium salt is ammonium chloride.

12. A method of acidizing a well comprising the steps of pumping a formaldehyde solution from one source into the well, simultaneously pumping a stoichiometrical 7. The method of claim 6 wherein said ammonium salt 5 is selected from the group consisting of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium carbonate, am-

. monium acetate, ammonium citrate, ammonium formate,

and tetraammonium ethylenediamintetraacetate.

8. The method of claim 6 wherein said ammonium salt is ammonium chloride.

9. A method of acidizing an oil-bearing earthen forma tion in a well having an annulus and tubular "members therein comprising the steps of, pumping an ammonium salt solution capable of reacting with formaldehyde solution to form a free acid down the annulus of the well, and simultaneously pumping a formaldehyde solution down the tubular members whereby said ammonium salt and said formaldehyde are brought together at apredeterequivalent amount of an ammonium salt solution capable of reacting with said formaldehyde solution to form a free acid from a second source into the well, combining said formaldehyde solution and said ammonium salt solution at the well head, and directing the acid formed to a predetermined position in the well for treating oil-bearing earthen formations therein.

13. The method of claim 12 wherein said ammonium salt is selected from the group consisting of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium carbonate, ammonium acetate, ammonium citrate, ammonium formate, and tetraammonium ethylenediaminetetraacetate.

14. The method of claim 12 wherein said ammonium salt is ammonium chloride.

15. A method of acidizing a well comprising the steps of, bringing a supply of formaldehyde to a Well site, bringing a supply of an ammonium salt capable of reacting with said formaldehyde to form a free acid to the well site, combining said formaldehyde and said ammonium salt together to thereby form a reactant solution, substantially immediately thereafter pumping said reactant solution into the well, and directing said reactant solution to a predetermined position in the Well for treating oil-bearing earthenformations therein.

16. The method of claim 15 wherein said ammonium salt is selected from the group consisting of ammonium fluoride, ammonium chloride, ammonium nitrate, ammonium sulfate, ammonium bromide, ammonium carbonate, ammonium acetate, ammonium citrate, ammonium formate, and tetraammonium ethylenediaminetetraacetate.

17. The method of claim 15 wherein said ammonium salt is ammonium chloride.

References Cited by the Examiner V UNlTED STATES PATENTS 1,999,146 4/35 Ambrose et a1 l6642 2,059,459 11/ 36 Hund et al 166-42 2,863,832 12/58 Perrine 2528.55 3,013,607 12/61 Bond et al. 166-38 CHARLES E. OCONNELL, Primary Examiner,

BENJAMEN HERSH, Examiner. 

1. A METHOD OF ACIDIZING OIL-BEARING EARTHEN FORMATIONS TO INCREASE THE PRODUCTIVITY THEREOF WHICH COMPRISES CHARGING A F ORMALDEHYDE SOLUTION INTO A WELL AS A FIRST REACTANT, AND, AS A SECOND REACTANT, AN AMMONIUM SALT SOLUTION CAPABLE OF REACTNG WITH THE FIRST REACTANT TO FROMA A FREE ACID, CONTACTING THE FIRST REACTANT WITH THE SECOND REACTANT THEREBY FORMING THE FREE ACID, AND DIRECTING THE ACID FORMED INTO AND THROUGHOUT THE OIL-BEARING EARTHEN FORMATION. 